Both groups dominated my teenage years during the 70's. And while both are on my Rock n Roll Mt. Rushmore (next to The Beatles and Black Sabbath), I gotta go with Led Zep. Only a few songs, like Four Sticks and Carouselambra, that I skip past.
But, I think 'Who's Next' is one of, if not the best, rock n roll albums of all time. Not one throwaway song on the album.
Live performances swing towards The Who. After about 1970, Zep sucked in concert. For one, they routinely made fans wait 1 -2 hours for them to take the stage. And their studio versions were so complex with Page's overdubs, it was nearly impossible to recreate live with just one guitar. Jimmy didn't help with his 20 minute guitar solos, screeching with a violin bow.